In advanced turbine engines, gas turbine parts in the hot gas path such as blades, vanes and outer air seals in the high pressure turbine and the low pressure turbine, are subjected to temperatures and loads that, over time, can distort the dimensions of these parts to the point that they deviate so substantially from the original equipment manufacturer's drawings and specifications that the parts are typically scrapped when the gas turbine engine is overhauled or repaired. In some cases, scrapping of the component and replacement with a new part may be driven by flight safety issues, but in other cases, the part is scrapped simply because there is no viable repair available.
An example of one such part is the stator vane segment 11 in the third stage of the low pressure turbine on the Pratt & Whitney PW4000 gas turbine engine, as shown in FIG. 1. Typically, a plurality of vanes 10 are clustered together to form a vane segment 11, of which there are a plurality in the set of third stage, low pressure turbine vanes for this particular engine. These particular vanes 10 are cast from a nickel-base alloy, such as Mar-M 247, an alloy well known in the art. They are installed in the engine by engaging by the forward outer shroud rail 12 and the aft ward outer shroud rail 14, as shown in FIG. 1, on the internal case rails of the low pressure turbine (not shown) of the engine. The inner shroud 16 includes an inner flange 18 which contains a bolt hole 20 that is used to bolt the vane segment 11 to an inner support (not shown) in the low pressure turbine. Due to thermal and aerodynamic loads, the inner shroud 16 may experience distortion such as displacement, or shifting, of the inner shroud 16, relative to the outer shroud 24, in the distortion direction 17, and elongation of the bolt hole 20 and a displacement of the center 22 of the bolt hole 20 in a distortion direction 17 relative to the outer vane shroud 24, which for the PW4000 would be clockwise from its original design location as viewed from a forward-looking-aft position, as shown in FIG. 1. This displacement of the center 22 of the bolt hole 20 is not isolated to one particular vane segment 11, in any engine set, as all vane segments 11 in a set may experience this type of displacement. The degree, or dimensional amount, of displacement is not constant from one vane segment 11 to another vane segment 11.
What is needed is a method and apparatus for restoring displaced features on a turbine vane segment for a gas turbine engine, such as a vane segment in a low pressure turbine, and more specifically, the inner shroud thereof relative to the outer shroud thereof to meet the original design position and dimensions.